The invention relates to a valve, in particular for admitting air into a motor-vehicle tank and extracting air from the same, as is described in claim 1.
Valves for extracting air from a fuel tank and admitting air into the same are known in the prior art. The operation of extracting air from a fuel tank and admitting air into the same has to be ensured during refuelling, operation and the standstill phase. Such valves are usually arranged between the fuel tank and the activated carbon filter (ACF). During refuelling, on account of the fuel fed and of a suction-jet-pump effect, a positive pressure is produced in the fuel tank, and this is fed to the ACF via the valve in order to ensure emission-free refuelling (onboard refuelling vapour recovery/ORVR). Moreover, the fuel vapours produced have to be fed to the ACF both when the vehicle is at a standstill and when it is travelling. When the vehicle is travelling, during the scavenging phases, the fuel vapours are taken by suction into the gas-feed stream of the internal combustion engine from the ACF, the valve protecting the fuel tank against a negative pressure being applied to the filter.
An opening and closing movement of such a valve or tank safety valve is usually made possible by a flexible elastomeric diaphragm arranged in the valve. Said elastomeric diaphragms have disadvantageous properties in respect of their permeability for hydrocarbon gases and a disadvantageous sensitivity to temperature. In particular with low temperatures, the flexibility or elasticity of elastomeric diaphragms with the necessary permeability is so low that this may result in the valve functioning inadequately or failing altogether. In view of the increasingly stringent limit values for hydrocarbon emissions for motor vehicles, in particular in the USA, there is thus a need for a valve which, even at low temperatures down to xe2x88x9240xc2x0 C., has satisfactory valve functioning and permeability properties.
The object of the invention is to provide a valve having the necessary permeation and temperature properties.
The object is achieved by a valve having the features specified in claim 1. Advantageous embodiments form the subject matter of the subclaims.
A valve according to the invention, in particular for extracting air from a fuel tank and admitting air into the same, has a tank duct leading to the tank and a second duct leading away from the tank, in particular leading to a filter or activated carbon filter, having a diaphragm for executing an opening or closing movement for respectively opening or sealing a through-passage from the tank duct to the second duct, the diaphragm consisting of metal, in particular of a metal foil. Surprisingly, a metal diaphragm advantageously has a low permeability for hydrocarbon gases which are contained in fuel vapours. In addition, the metal diaphragm according to the invention has an advantageous low temperature dependency in respect of its mechanical properties, in particular of its flexibility, elasticity and permeability for gases. As a result, the dependency of the functional values of the valve and of the permeation of gases on the temperature can be minimized and preferably eliminated.
Basically all metals which can be rolled out as a foil and/or sufficiently thinly are suitable for the diaphragm. High-grade steel and copper/beryllium have proven particularly preferred as materials for the diaphragm.
According to a preferred embodiment, the diaphragm has a thickness in a range of from 20 xcexcm to 40 xcexcm. In this thickness range, the diaphragm has a sufficiently low permeability along with advantageous mechanical properties, in particular high elasticity and flexibility.
According to a further preferred embodiment of the invention, the valve comprises an additional sealing device for sealing and/or closing the through-passage between the tank duct and the second duct. The sealing device is arranged on the diaphragm.
The sealing device preferably consists of an elastomeric material which allows a good sealing action. The sealing device here need not have a low permeability in relation to hydrocarbon gases since the sealing function in relation to the surroundings is provided by the diaphragm. The sealing device is preferably secured, for example adhesively bonded or vulcanized, in the centre of the diaphragm.
According to a further preferred embodiment of the invention, the tank duct and the second duct are connected to one another in addition by a one-way valve, which opens when the gas pressure in the second duct is higher than the gas pressure in the tank duct. This allows gas from the filter, in particular in the form of an activated carbon filter, to be admitted into the fuel tank.
The one-way valve is preferably designed as an umbrella-type mushroom valve.
According to a further preferred embodiment, the diaphragm is designed such that, for the opening and closing movements, it allows an expansion by a predetermined distance., This allows a larger opening displacement of the diaphragm and thus a larger free opening cross section of the through-passage.
At least part of the diaphragm may advantageously be designed with corrugations which run essentially perpendicularly to the expansion direction. Such corrugations can be pressed into the diaphragm or the diaphragm foil by a moulding step and allow a considerably larger displacement of the diaphragm.
According to a further preferred embodiment, the diaphragm is of circular design and, on its outer circumference, is retained in a gas-tight manner by way of a sealing ring on at least one sealing surface of a valve housing. The sealing ring here may be pressed onto the valve housing by a clamping cover such that it positions the diaphragm against the sealing surfaces in a gas-tight manner.
The invention is described by way of example hereinbelow with reference to a preferred embodiment, in which: